Biomarkers in Tubifex tubifex for the metalaxyl and metalaxyl-M toxicity assessment in artificial sediment

Efficacy and potential environmental risks should be considered when applying enantiopure pesticides. In this study, Tubifex tubifex and its oxidative stress biomarkers were assessed for the toxicity of metalaxyl and metalaxyl-M in sediment. The toxicity assessment was conducted with artificial sediment and reconstituted water. Five test concentrations (from 0 to 100 mg/kg) were set for the short-term (4 days) exposure. The long-term (28 days) exposure was conducted with the environmental concentration (from 0.5 to 5 mg/kg). For the short-term exposure, the increase of superoxide dismutase (SOD) activity was observed, and a clear concentration-response relationship was found in the metalaxyl treatments. The decrease of catalase (CAT) and glutathione peroxidase (GPx) activity could be caused by oxidative stress. The decrease of glutathione (GSH) content and the increase of glutathione-S-transferase (GST) might be due to antioxidation defense and detoxification mechanisms. The increase of malondialdehyde (MDA) might be due to the saturation of antioxidant systems and the accumulation and toxicity of contaminations. In the long-term exposure, the changes of biomarkers in T. tubifex reflected the oxidative stress and detoxification metabolisms. GSH and the related enzymes were important in detoxification processes and involved in the oxidative stress in toxicity mechanism. The long-term direct contact bioassay is sensitive and appropriate to reflect the lower concentration of contaminants.